Electric furnace.



A. E. GREENE. ELECTRIC. FURNACE.

APPLICATION FILED NOV. 12, 1909.

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ELECTRIC FURNACE.

APPLICATION FILED NOV. 12, 1909.

1,070,337. Patented Aug. 12, 1913.

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ELECTRIC FURNACE.

APPLICATION FILED NOV. 12, 1909. 1 070 337, Patented Aug. 12, 1913.

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ELECTRIC FURNACE.

APPLICATION FILED NOV. 12,1909.

Patented Aug". 12, 1913.

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cfllerizarea/a6 UNITED sTArEs PATENT OFFICE.

ALBERT EDWARDS GREENE, OF CHICAGO, ILLINOIS, ASSIGNO-R TO AMERICAN ELEC- TRIO SMELTING AND ENGINEERING COMPANY, OF ST. LOUIS, MISSOURI, A GOR- POBATION OF MISSOURI.

ELECTRIC FURNACE.

.Specification of Letters Patent.

Application filed November 12, 1909. Serial No. 527,691.

To all whom it may concern.-

Be it known that I, ALBERT E. GREENE, a

' citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented certain new and use ful Improvements in Electric Furnaces, of which the following is a specification.

My invention relates to electric furnaces and metallurgical processes to be practised therewith. whereby the temperature of the material under treatment and the composition of the gas maintained in contact with the material are controlled independently of one another.

Broadly the object of the invention is to provide suitable apparatus for the refining of metals, for the extraction of metals from mattes and ores. and for the treatment of materials in general requiring combined heat treatment and chemical action, and the several types of apparatus set forthherein for such ends, all combine a means of electric heating and a control of gas used in the furnace chamber.

More specifically this invention consists in means for maintaining electric arcs in proximity to the material as a source of heat,

and means for stretching or drawing out such arcs, to obtain uniform heating, and at the same time utilizing a gas toreact with the material therein. The result is a control of the gaseous reagents used, or in certain cases of the atmosphere maintained in the furnace, more or less independently of the control of temperature, and thereby making possible reactions otherwise not obtainable, and also increasing the rapidity of treatment and efficiency in general.

In the conversion of metals and mattes by the processes hitherto in general use, the heat is controlled by combustion, or the heat of combustion when excessive may be modi fied by certain endothermic reagents. These processes are unavoidably inefficient in that it is not practicable to thus control the composition of gas and temperature independently, and the result is a loss of material either by oxidation or a failure to completely extract it by reducing agents, as well as to an ineflicient elimination of the impurities. T hisinvention is designed to supply apparatus in which the above losses may be averted.

In the converter process for extracting copper matte, it is impossible to get a satisfactory elimination of iron and sulfur, and at the same time leave the product free from oxids and traces of sulfid. The apparatus of this invention is also applicable to processes by which such difliculties are overcome. I In the refining of iron and steel to elimmate phosphorus and sulfur it is desirable, in certain cases, to maintain a high temperature over the surface of the slag while subecting' the material to the action of a gaseous reagent, and this invention provides means therefor.

In the extraction of metals from their ores few of the processes now in use accomplish the elimination of a given impurity, or the extraction of a metal, without leaving some of the impurity to be extracted by another process or some of the metal in a by-product, which metal can be saved only by further treatment. For example, the common processes for extracting copper from s ulfid ores only partially eliminate the, sulfur in the roasting and reduction processes and leave the remainder to be removed in the refining furnace. In the roasting of sulfid ores the elimination of sulfur is' incomplete. Moreover the result of the roasting is to convert the larger part of the sulfids into oxids. In the treatment of iron ores containing phosphorus and sulfur these elements are invariably retained in the pig iron, which is the first product of reduction. The proh- 1 lem of reduction of iron pyrite ores has been -left for solution until the diminishing supply of oxid ores will create a need for a satisfactory method of getting iron from them.

In my copending applications Serial No. 426,334, filed April 10th, 1908, and Serial No. 488,360, filed April 7 th, 1909, I have disclosed a metallurgical process suitable for eliminating an impurity such as sulfur by a selective oxidation while the desired metal is retained reduced.

It is one of the objects of this invention to provide suitable apparatus for carrying out processes of this nature and such apparatus may be of the two types,rotary or Stirring furnaces and shaft furnaces herein after described.

In one of its forms this invention contemlates to the use of polyphase arcs-either in single combinations between separate pairs of electrodes, or with all the arcs extending to a neutral point or electrode.

Another feature relates to impinging the arc or arcs on the surface of the material,

and in certain cases of using the bath as one electrode. Where polyphase current is used the material under treatment may be used as the neutral, or the neutral point may be maintained at a point where the several gas currents which direct the arcs meet.

The invention also provides means for maintaining arcs over the surface of the bath after the preliminary gaseous treatment.

Having considered several of the essential features of this invention broadly, I will now describe these in detail and also several of the embodiments of the invention by reference to the accompanying drawings.

Figure 1 is a vertical central section of a Bessemer converter, modified for electric .heating in accordance with this invention.

Fig. 2 is a side elevation thereof, partly in section. Fig. 3 is a vertical central section of a copper converter modified in accordance with this invention. Fig. 4 is a side elevation thereof. Fig. 5 is a central vertical section of a modified form of the invention. Fig. 6 is a side elevation of the structure shown in Fig. 5. Figs. 7 and 8 are transverse and longitudinal sections, respectively,

of an open hearth furnace embodying thisinvention. Fig. 9 is a horizontal section of a modification of the invention. Fig. 10 is a vertical section of one end of the furnace shown in Fig. 9. Figs. 11 and 12 are horizontal and vertical sections, respectively, of a further modified form of open hearth furnace. Fig. 13 is an end view of a rotary furnace embodying certain features of this invention. Fig. 14 is a vertical section of a further modified form of rotary converter. Figs. 15 and 16 are vertical, longitudinal sectionsof different types of rotary cylindrical furnaces embodying this invention. Figs. 17 and 18 are vertical, longitudinal sections of apparatus adapted for the continuous treatment of ores or other material. Fig. 19 is a vertical section of a blast furnace of the type employed for reducing iron electric converter.

ores, modified in accordance with this invention. Fig. 20 is a vertical section of a type of furnace suitable for reducing copper ores; and Figs. 21 and 22 are vertical sections at right angles to each other of an induct-ion furnace modified in accordance with this invention.

One of the most important embodiments of the invention is in what may be called an This type is applicable to the treatment of iron, steel, alloys and mattes, and in certain of its modifications to ores, such as lead and copper ores.

The electric converter of this invention in general embodies a means of heating electrically and a means of forcing gas through the converter in contact with the arc flame, and also in contact with the material to be treated. In the processes now in general use for converting steel and copper, the vessels are large and very expensive, and one of the most importantpoints of advantage of this invention is that it does not necessitate replacing such apparatus by other apparatus of aradically different nature, but on the contrary is a direct modification of the present types of furnaces.

Referring to Figs. 1 and 2, and 3 and 4, two types of electric converters are shown therein, the former adapted more particularly to the conversion of pig iron, and the other more particularly to the conversion of mattes. In Figs. 1 and 2, 1 is the chamber of the converter into which the metal to be converted is placed. Connecting with this chamber 1 are enlarged twyers 2, and at the upper end of these twyers entering through the pipe-fitting 4, are the electrodes 3. The electrodes 3 are insulated from the metal work by the insulating bushings 5. Fig. 1 shows also an electrode 6, which may be employed if desired, entering the vessel at a level slightly below that of the metal in the furnace chamber. The blast pipes 7, leading to the twyer pipes 4, connect with a pipe 12 which leads to the trunnion 9, and in which there is a valve 11 for controlling the pressure of the gas admitted through these twyers against the top surface of the metal. In the bottom of the converter are shown twyers 8, which connect with the wind box 10, which is in turn connected to the-trunnion 9 through the pipe 12.

Referring to Figs. 3 and 4, the twyer holes 21, similar to those in Figs. 1 and 2, connect with the furnace chamber in which the charge of the metal is contained. The mouths of the twyers are enlarged where they enter the chamber 20, and by tilting the vessel the molten metal can be made to enter the enlarged mouth of the twyers. When the vessel is so tilted, the arc may be started between the electrode 18 and the metal 19 by moving the electrode into proximity to the metal. The axis of the electrode 18 is shown as inclined with respect to the axis of the twyer hole 21, and thereby provides means to start the are without an excessive length of electrode being required to reach down to the metal bath. The electrode 22 enters the vessel through the insulating bushing 23, and-at'a height such that it may either be maintained in contact with the metal bath which may thereby serve as one electrode, or it may be maintained above the surface of the bath by tilting the vessel, and thereby provide means for maintaining arcs between the electrodes 18 and 22. The electrodes 18 enter the .twyers through the bushings 24 which prevent contact of the electrodes with the elbows 17. The pipe 16 which leads from any suitable source of supply of gas connects with the twyers 21 through the pipe connections 15 and 17. The connection of the pipe 16 through the trunnion 9 is not shown as any suitable means for accomplishing this may be used. Entering the chamber 20 is shown a twyer 13 which serves to admit gas under pressure at or below the surface of the metal according as the vessel is tilted more or less. This twyer 13 connects with a pipe 14 which leads to a suitable source of gas, and which may or may not be the same source as used for the pipe 16. The exhaust gases leave the vessel through the exhaust opening 26.

Referring to Figs. 5 and 6, there is shown a modified type of electric converter somewhat similar to an open hearth furnace. The metal 122 is contained in the chamber 123, and is subjected to the action of the electric are extending between the electrode 124 and the metal bath 122 entering through the twyer 25. The length and direction of the arc, as in the figures previously referred to, is controlled by the gas forced in through the pipe 26 around the electrode 124, and the tendency is for the arc to be stretched by the current of gas to the side of the furnace opposite to the electrode 124. On the opposite side of the furnace from the electrode 124 are shown electrodes 27 which serve for maintaining arcs over the surface of the bath where it is desirable to heat the bath without entrance of gas into the furnace chamber. The electrode 27 is so arranged with regard to the bath that it may dip into it if desired, and therefore serve as one means for starting the arc. The spout of the furnace is shown at 29, and one of the doors for admitting material into the furnace is shown at 30. The exhaust gases leave "the furnace through the exhaust hole 31. This furnace is preferably of the tilting type.

In Figs. 7 and 8, and 11 and 12, are shown modifications of an open-hearth furnace for electric heating of the bath by the use of electric arcs extending over the surface of the metal. furnaces are arranged so that the electric heating may be used separately or in conjunction with the usual means of supplying gas to the open hearth furnace. In Figs. 7 and 8 the electrodes are shown at 32 entering the furnace through insulating bushings 33 above the surface of the bath 34. The gas ports are shown at 35 slightly below the level of the air ports 36. The doors 3T-serve for the entrance of material into the furnace chamber, and the spout 38 serves for drawing off the metal from the furnace. In Figs. 11 and 12 the electrodes 41 are so located that the arc traverses the chamber above the metal bath in the same direction as the gas from the ports 36 and 35. The pipe 43 leads from a source of gas and connects with the twyers 44, which are located slightly below the level of the electrodes 41, and serve for the admission of suitable gas between the arcs and the bath.

In Figs. 9 and 10 are shown two views of a furnace in which the arc is directed by means of a current of gas down against the surface of the bath. The electrodes are shown at 45 entering through the insulating bushings 46, and spreading out inside the furnace in front of the twyer pipes 47 which connect by means of pipes 48 to any suitable source of supply of gas. v

Fig. 15 shows a rotary cylinder with the chamber 51 lined with suitable refractory material. The opening 50 to this chamber may be made air tight after the material has been placed in the chamber, and the cylinder is provided with means for rotation on the roller bearings 53. Opening into the chamber 51 are pipes 52, through which enter the electrodes 54 out of contact with the pipes 52. Connecting with the pipes 52, are gastight joints 55, which allow the cylinder to rotate independently of said joints. The electrodes 54 enter through insulating bushings 56. The joints 55 are connected by means of valve pipes 57 to any suitable source of gas or suitable exhaust apparatus, as the case may be.

In Fig. 16 is shown a cylinder of similar construction to that in Fig. 15, except that the ends of the cylinder do not rotate with the cylinder body, and are separate from it. In the heads 58 the electrodes 54 are placed at equal distances from each other and around the gas inlet 52. This construction makes possible the use of polyphase currents for blowing the arcs out into the furnace chamber. The arcs may extend from the electrodes 54 at one end of the cylinder to the corresponding electrodes 59 at the opposite ends of the cylinder. Or the arcs may extend from the three electrodes at one end of the cylinder coming together in a common neutral point, and by the use of gas blown through-the inlet 52 the arcs may be stretched out into the furnace chamber. The gas pipes 60 serve for the entrance and electrodes for use of three phase currents,

and Fig. 14 shows the arrangement used for blowing a single phase are away from the electrodes.

In Fig. 17, showing another modification of rotary cylindrical furnaces, 72 is the rotating part of the cylinder. The electrodes 73 enter the stationary head 70 through the insulating bushings 74 and are located in any desirable manner for the use of single phase or polyphase current. At the opposite end of the cylinder the head 71 contains electrodes 75 located for maintaining the arcs from the electrodes 73 through the furnace chamber. Through the head 70 at the lower end of the cylinder the gases enter through the pipe 76. The joint 77 connecting therewith, leads from any suitable source of supply of gas, and the twyer 78 which enters the joint 77 may be used for the supply of different gas from that'entering' through the pipe connecting with 77.

At the upper end of the cylinder the gases are removed through the exhaust opening 80. The entrance of material into the cylinder is accomplished from the hopper 81 in combination with the screw 82 and the feed of material into the cylinder may thereby be regulated. The exit of material from the cylinder takes place through the opening 79.

.The rotation of the cylinder and the mechanical operation in general is carried out by means well known in the art. I

In Fig. 18 is shown a further modification of a rotary furnace and a combination of furnaces for utilizing the combustible gas from one chamber by burning it in another chamber to heat the material therein. The cylinder 83 in this figure is similar to that shown 'in Fig. 17, and connects at its upper end by means of the stationary joint 87 with the cylinder 84. The material enters the cylinder 84 by. means of the hopper 81 and I screw 82, and passes froni'the cylinder 84 through the passage 87 into the cylinder 83, and from the cylinder 83 it may pass into any suitable furnace, such as shown at 85 for melting the materials treated, or may be disposed of in any desired manner after leaviiig the cylinder '83. Entering the cylinder 84 through the head is a nozzle and.

pipe 86 for the supply of gas to support combustion in the cylinder 84, and by this means to heat the material passing through the cylinder 84. The opemng 76 into the cylinder 83 which connects with'any suitable source of gas serves for the supply of gas to react with the material in cylinder 83,

while under the influence of electric heat generated from the arcs extending between the electrodes 74. For example, in this cylinder 83 certain elements maybe oxidized while; the metal desired may be retained in a reduced state. When this takes place at a temperature below the fusion point of the material treated, a final melting and separation of the oxidized and reduced elements may take place in the furnace shown at 85. Figs. 19 and 20 show the method of applying this invention to blast furnaces, the latter showing the type ordinarily used for smelting copper and lead modified according to this invention. 94 is the upper part of the furnace shaft. 91 is the bosh connecting therewith, and 90 is the metal chamber beneath the bosh where the smelting of the material is accomplished. 92 are the enlarged twyers into which the electrodes 93 enter through the bushings 96, which serve to insulate them from the blast pipe connection 97 connecting with the bustle pipe 98. 99 is the tapping spout. The pipe 95 serves for the exit of gases from the furnace.

Figs. 21 and 22 show the-combination of the features of this invention with a furnace of the induction type. shown at 105 and 106.- The electrode 105 enters the furnace chamber through the blast pipe connection 102. 107 is a door for the entrance of material into the furnace chamber. 103 is a pipe for the removal of exhaust gases. 104 is the core, around which the coils 108 are. placed. The small channels surrounding these cbils are shown at 100. The tapping spout for the furnace is shown at 110. In case it is desired to use the metal as one electrode, the electrode 111 connecting with the metal bath serves as one terminal of the passage of current.

The application of the apparatus and the use of thesame for the conversion of pig iron into steel, and for the removal of phosphorus and sulfur will now be described.

Theapparatus is so constructed that the metal may be blown by air or other suitable oxidizing agent to any desirable point of eliminatlon of carbon, and may subsequently be blown with a reducing gas or a gas of such composition as to remove the undesired elements without oxidation of the metals of the bath which it is desired to retain reduced. For the elimination of phosphorus and sulfur, a basic slagis required to hold these elements after elimination from themetal, and the linin of the vessel must, in such instances, be 0 the basic character in order to avoid corrosion by the basic slag.

version may not supply suflicient heat in re- The electrodes are acting with the impurity in the bath to maintain the desired temperature, the means disclosed in this specification for maintaining long arcs may be resorted to. To start the arc, the vessel may be tilted so that the metallic bath and the electrodes may be brought in proximity to each other, and the arc started in this manner. After starting, the arc may be stretched out by tilting back the vessel while raising the voltage applied to the electrodes as may be required. It may be advantageous in certain cases to use the neutral electrode in contact with the metallic bath to start the arc, and in the case of polyphase arcs being used the neutral electrode may be used to prevent shifting of the neutral point. In starting the arc, the tendency is for the arc to assume the shortest path between the electrode and the bath. By blowing in the gas around the arc, the arc is made to stretch out over the surface of the bath to a point distant from that nearest the electrode. By this means the heat of the arc is communicated to the gas, and simultaneously to the metal or material in the furnace chamber, and to a uniform degree, avoiding thereby extremely high temperatures in limited areas of the bath. In order to hasten the elimination of carbon, the blast of gas may be forced through the bottom twyers as well as through those through which the electrodes enter. By means of the valve connecting the electrode twyers to the source of supply of gas, it is possible to regulate the pressure in these latter twyers, and this is necessary since the pressure required to maintain the static pressure of the bath of metal would be too reat for use above the bath. After the car on has been eliminated as far as desired, the elimination of phosphorus and sulfur may next be accomplished. As it is desirable to eliminate both of these elements in a single slag, it is necessary to keep any oxid of iron or other metals in the bath from being present in this slag. The flux for accompllshing this would preferably consist of lime and fluor spar. The gas employed in the treatment is blown into the furnace chamber around the electrode and carries the are down over the surface of the bath, making it impinge on the fluxing materials used. This is an important feature of this invention since it enables the treatment of the metal in the presence of a flux with asuitable gas for eliminating the impurities which thereupon pass into t e slag.

In certain instances, it may be deslrable to maintain the electric discharge over the surface of the bath after the blowing has been stopped for the purpose of eliminating gas absorbed in the metal. In bottom blow converters where it is desired to do this, the bottom blow twyers may be placed in a portion only of the bottom of a furnace, as shown in Fig. 3, so that the metal may be held without running into these twyers after the blast has ceased.

In the operation of the furnaces shown in Figs. 7 to 12, the treatment is quite similar to that described above. The combination of electrodes in the chamber of anopen hearth furnace for maintaining an electric arc with the gas ports of that furnace afl'ord means for the treatment of the charge while passing a reducing gas through the furnace, and in this way greatly aiding in the elimination "of phosphorus and sulfur from the metal.

Figs. 3 and 4 show a modification of the type of the converter used in converting mattes. modification is designed for the treatment of copper mattes and mattes in general including nickel. In using this apparatus for converting mattes, it is especially advantageous for the purpose of maintaining the temperature ofthe large amounts of metal oxidized and held in the slag above the metal bath. By processes of selective oxidation, it is possible in this apparatus to oxidize the sulfur and iron and other undesirable impurities, while retaining the copper or other metal, as for example, nickel in a reduced state. By this means, an attractive method is offered for the separation of nickel from ferro-nickel pig and from nickel mattes. The iron may be oxidized and slagged off in combination with suitable fluxes, while the nickel is retained as'metal. In the treatment of mattes, the use of a twyer located at about the level of the metal is of a special advantage in obtaining contact between the metal and the gas where very large amounts of slag are produced. Tilting the vessel will serve to obtain the desired relation of this twyer to the level of the metal.

The application of this apparatus. in the continuous treatment of ores will now be described.

Apparatus for the continuous treatment of materials may be either in the form of rotary cylindrical furnaces shown in Figs. 15 to 18, or furnaces having other suitable stirring means for getting contact between the gas and the ore under the influence of the arc, or may be of the shaft furnace type with blast connection, shown in Figs. 19 and 20. These furnaces are applicable to the treatment of ores and material in gen-- eral, but are preferably designed for the treatment of ores according to selective processes. For example, in the treatment of copper sulfid ores, this apparatus affords a means of eliminating the sulfur from such ores in the form of a gas, while obtaining the copper in a reduced state. Similarly, in the treatment of iron ores containingphosphorus and sulfur, this apparatus affords a means of eliminating the phosphorus and sulfur by means of a gas, and leaving the metal in a reduced state. This may not require temperatures high enough to satisfactorily melt the reduced iron, and therefore a suitable melting furnace might well be used in combination with such furnaces for suitably separating the metal and the other elements of the ore, as shown in 18. I To make clear the operation ofthe apparatus, assume that it is desired to treat a copper sulfid ore for the purpose ofeliminating the sulfur, and obtaining the copper in a reduced state in a continuous operation. Apparatus suitable for this end, is shown in Fig. 18. The ore is fed into the rotary cylinder by means of the hopper and screw. In passing through this cylinder, the ore becomes heated by the combustion of the gas entering from the cylinder next below. ir is blown in to the upper cylinder to burn the combustible gas. The. heated material from the upper cylinder enters the lower cylinder, and is there treated under the influence of electric heat generated by the arcs in this lower cylinder and the gas forced in at the lower end of this lower cylinder. This gas accomplishes the elimination of the sulfur and leaves the metallic copper in a reduced state mixed with other elements, such as silica, fro-m which it is necessary to separate the copper. This separation may be accomplished in the furnace 85 situated below the lower cylinder 83, by melting the metal and separating it from the other remaining ingredients of the ore. This is preferably done under the influence of electric heat, and in a furnace in which the atmosphere is of the desired nature, reducing in this instance.

In the manufacture of cement, this appa' ratus ofiers an effective means of accomplishing the results desired, namely,the elimination of carbon dioxid, and the sintering of the elements required to form cement. The types of rotary electric furnaces shown in Figs. 15 and 16, serve for the treatment of materials in a closed chamber which may or may not have gas forced through it to assist in the desired reactions. Such apparatus is suitable, for example, for the calcining of materials like carbon, limestone, clay, etc. The stirring action obtained in these rotary furnaces is an essential feature of the invention. The means forlobtaining the stirring action in the material is not limited to rotation of the furnaces, but other suitable means to stir the material, while under the influence of the electric arc may be used. It is understood that the invention is not limited as. to the means of accomplishing the stirring action.

In applying the invention to blast furnaces, the operation of the furnaces of this 65 type is quite similar to the operation in the above described types. By blowing in the gas around the arc, ,and making the arc impinge on the material in the smelting chamber of the furnace,, efficient melting of the material is thereby accomplished, and the utilization of the hot gases whose composition may be controlled prior to their entrance into the furnace, is effected.

One other embodiment of the invention has been shown in Figs. 21 and 22 in a furnace of the induction type. It is well lmown that although the induction furnace affords effective means of generating heat in the metal, it does not provide or efiectively heating a flux or slag lying on top of the metal. It is the object of this embodiment to combine with the efficient means provided by the induction furnace for heating the metal, the means described herein for heat-. ing and treating the slag above the metal.

Although having described in detail so eral of the embodiments of this invention, it is understood that its features may be combined in numerous other ways, and that it is applicable in other types of furnaces than those described. X

I claim:

1. In an electric furnace, the combination with a tilting furnace chamber suitable for inclosing material for treatment, of an electrode in the side wall of said chamber above the surface of said material, means for maintaining an electric are between said electrode and said material, and means for tilting said chamber and thereby bringing 100 said material in proximity to said electrode to start the arc.

' 2. In an electric furnace, the combination with a tilting furnace chamber suitable for inclosing material for treatment, of an elec- 105 trode in the side wall of said chamber above the surface of said material, means for maintaining an electric are between said electrode and said material, and means for passing a current of gas through said chamber and 110 thereby drawing out said are.

3. In an electric furnace, the combination with a furnace chamber suitable for inclosing material for treatment, of electrodes projecting into said chamber from opposite 115 sides thereof, means for successively maintaining an electric are above the surface of said material between one of said electrodes and said material and between said opposite electrodes, respectively.

4:- In an electric furnace, the combination with a furnace chamber suitable for inclosing material for treatment, of an enlarged twyer opening into said chamber above the surface of said material, an electrode within 125 said twyer, and means for maintaining an electric are between said electrodes and the material under treatment.

5. In an electric furnace, the combination with a furnace chamber suitable for inclosing material for treatment, of a plurality of electrodes mounted at one side of said chamber, means for maintaining a polyphase electric discharge from said electrodes to said material, and means for supplying a current of gas for lengthening the arcs produced by said electric discharge.

6. In an electric converter, the combination with a tilting furnace chamber, of an en- 10 larged twyer located above the surface of the material in said chamber, an electrode in said tWyer, and a twyer near the bottom of the chamber at one side thereof.

Signed by me at Washington, D. (3., this 12th day of November, 1909.

ALBERT EDWARDS GREENE.

Witnesses:

GEORGE E. FOLK, GEO. S. LIVINGSTON. 

